“If it’s never new and it doesn’t get old,” the singer tells his audience, “it’s a folk song.” Llewyn Davis (Oscar Isaac) has just finished performing the traditional blues number “Hang Me, Oh Hang Me” for a sparse crowd at the Gaslight Café in New York City’s Greenwich Village in early 1961. Back then, before Bob Dylan revolutionized everything, and Peter, Paul and Mary popularized Dylan’s “Blowin’ in the Wind,” the folk scene was really two scenes. Pete Seeger and the Weavers, and their more homogenized avatars The Kingston Trio, filled the concert halls. And in tiny coffee shops, pursuing their more austere art, were “neo-traditionalists” like the Irish balladeers the Clancy Brothers and Tommy Makem, the dulcimer-strumming Kentucky lass Jean Ritchie and, imparting a feral growl to old Anglo ballads, Brooklyn’s own Dave Van Ronk — the rough inspiration for the fictional Llewyn Davis in Joel and Ethan Coen’s ornery, dramatically confounding, lovingly scored new film.

Llewyn has made one album as part of the folk duo Timlin & Davis, before Timlin killed himself by jumping off the George Washington Bridge, and then a solo LP that has sold in the dozens of copies. With no fixed abode, he’s obliged to beg for couch space in the apartments of friends — a daunting task for Llewyn, since he’s a plebeian pain in the ass. As foulmouthed as any Merchant Marine (he has shipped out twice before to finance his art), and an off-putting mixture of self-absorption and self-righteousness, Llewyn has the aptitude for success but not the attitude. He alienates nearly everyone in a position to advance his career, or to give him a few nights’ lodging. Who’d want to get inside Llewyn Davis?

That’s the challenge the Coens set for their first film since the smash hit and Oscar contender True Grit. As if to atone for that Western’s ingratiating mass appeal, the brothers have created a character who’s hard to love and a bit of a chore to invest in for an hour and 45 minutes. Like the old songs in his repertoire, he’s familiar, not new, but he quickly gets old and tiresome. And a series of internal contradictions. For a boy raised on the mean streets of Queens, Llewyn has few street smarts. Advice to folks new to the big city: When you step into an alley and a man in the darkness makes threatening remarks, don’t walk toward him.

Llewyn’s unlucky streak extends to all those who inhabit his orbit. Sleeping over at the home of Columbia professor Mitch Gorfein (Ethan Phillips) and his wife Lillian (Robin Bartlett), whose hospitality he routinely abuses, Llewyn lets their tawny cat sneak out of their locked apartment and spends much of the movie searching for the critter. You could call Llewyn the black cat in the path of a crippled blues man (John Goodman) and a near-mute actor (Garrett Hedlund) with who he shares a car trip heading for Chicago. Llewyn’s best friend Jim Berkey (Justin Timberlake) gets him studio gigs, unaware that the ingrate has been sleeping with Jim’s wife Jean (Carey Mulligan). And now Jean is pregnant. “Everything you touch turns to shit,” she astutely tells Llewyn. “Like King Midas’s idiot brother.”

Lost musical causes of the ’60s have recently preoccupied some of the finest writer-directors. Last year, David Chase, creator of The Sopranos, fashioned the drama Not Fade Away around four Jersey boys who start a blues band. They had no hits, and no wonder: the guys displayed no original musical talent. Chase’s film too was a major disappointment. No question that Inside Llewyn Davis is far superior hymn to the loser ethos. Its excellent cast gives at least as much humanity to the characters as the script allows; and Bruno Delbonnel’s cinematography captures the soul-contracting frigidity of a New York winter. Imagine the cover photo for the album The Freewheelin’ Bob Dylan — the singer huddling for warmth on a chilly Village street with his girlfriend Suzy Rotolo — raised to living camera art.

Unlike the talent-deprived guys in Not Fade Away, Llewyn does have an easy mastery of his guitar and a gift for invigorating old songs. But he also radiates a surliness associated with the other urban pose of the period: he’s a beatnik-come-lately. When Lillian Gorfein pleasantly observes, “I thought singing was a joyous expression of the soul,” Llewyn glowers at her like an imperious teacher at his dumbest student. And when an Appalachian singer steps to the Gaslight microphone, Llewyn rattles the walls with obscene insults that climax in his declaration, “I f—in’ hate folk music!” See, he’s not so much a music purist as a Llewyn Davis purist.

Some filmmakers might have chosen to dramatize the folk-pop era by fictionalizing the early success of Peter, Paul and Mary. They appear here, in fetal form, as Jim, Jean and Troy Nelson (Stark Sands); Albert Grossman, the entrepreneur who put the trio together, shows up as Gate of Horn manager Bud Grossman (F. Murray Abraham). But not the Coens. Could it be that they dreamed up Llewyn as a subordinate character to dance mischievously around Jim and Jean, then saw him commandeer the narrative by the sheer force of his truculence?

Having put this human exasperation at the center of the story (the other characters are mere satellites with a few scenes each), the Coens constructed an episodic format that is as loose as, say, Jack Kerouac’s Beat novel On the Road, and which depends utterly on the distinctiveness of the eccentrics who people each episode. In fact, the strongest section — the car trip with Goodman and Hedlund (who played Dean Moriarty in the On the Road movie that showed at Cannes last year) — is also the least essential to Llewyn’s own tale. For ostensible continuity, the brothers summon that darn cat to materialize or vanish at intervals. This is a device unworthy of the brothers’ usual ingenuity, though it does link Inside Llewyn Davis to another 1961 pop-cultural artifact: the film of Breakfast at Tiffany’s, in which the true soulmate of Holly Golightly (Audrey Hepburn) is a cat named Cat.

Llewyn remains something of a misfit in the Coen universe, where decent misfortunates (Billy Bob Thornton’s betrayed husband in The Man Who Wasn’t There, Michael Stulberg’s hapless professor in A Serious Man) are easy marks for those with sharper instincts. Llewyn is more predatory than victimized; his angry flailing leaves collateral bruises on sympathetic bystanders. In the old definition of the Yiddish words schlemiel and schlimazel — the first being the fellow who always spills his soup, the second the guy he invariably spills it on — Llewyn is the schlemiel without a clue, and no cause but himself.

Except for Hedy West’s folkish “500 Miles” and the novelty tune “Please Please, Mr. Kennedy (Don’t Shoot Me into Outer Space),” all the songs here are traditional. As Joel Coen says in the press notes, “If you trace it back far enough it’s all Americana, the same kind of music, the same family tree, the same species of song we used in O Brother, Where Art Thou?” That larkish comedy-musical, which played at Cannes 13 years ago, was based on Homer’s Odyssey and set in the ’30s South; it leaves its imprint all over Inside Llewyn Davis, not least in the name of one important character: Ulysses.

T-Bone Burnett, the maestro of O Brother (and an Oscar winner for the Jeff Bridges Crazy Heart), supervised the music. Sung live by the actors, it resonates with lyrical acuity. The version of “500 Miles” by Mulligan, Timberlake and Sands has a sonorous sweetness beyond the Peter, Paul and Mary version. And as nagging as Llewyn can be offstage, he too comes to life when he sings: the lustrous, aching “Dink’s Song” (“Fare Thee Well”) three times, the Van Ronk favorites “Green Green Rocky Road” and “Cocaine” and, finest of all, the cover of a song popularized by Joan Baez,”The Death of Queen Jane” — a beautiful rendition that, you might think, would get Llewyn booked into any night spot he auditioned for. In the movie’s strongest scene, Llewyn sings Ewan MacColl’s “Shoals of Herring” for his catatonic father. During these numbers, Isaac (born in Guatemala and raised in Miami) doesn’t discard Llewyn’s prickly personality; he integrates it into the vocal performance. This is acting-singing of the highest caliber.

The film’s U.S. release is being held for December, the thick of awards season. Will fans of folk music have to wait until winter for the CD as well? We hope it’s available sooner, not only for the sonic pleasure that awaits — it’s not new music and it never gets old — but also because Inside Llewyn Davis is more deserving of a Grammy than an Oscar. Problematic movie, great album.